This application relates to the identification and synthesis of novel hormones. In particular it is concerned with hormones involved in the biochemistry of reproduction in mammals.
Human reproduction is controlled by the hypothalamic-pituitary-gonadal axis appearing early in fetal development. Luteinizing hormone releasing hormone (LHRH), also termed gonadotropin releasing hormone (GnRH), is a decapeptide of known structure and represents a key molecule in this control circuit. It is produced by hypothalamic neurons, secreted in a pulsatile manner into the capillary plexus of the median eminence and effects the release of luteinizing hormone and follicle stimulating hormone from gonadotrophic cells in the anterior pituitary. LHRH or LHRH-like immunoreactivity has also been found in gonadal tissue placenta, [G. Khodr et al., "Science" 207: 315-317 (1980) and J. Gautron et al., "Mol. Cell. Endocrinology" 24: 1-16 (1981)] and the central nervous system, thereby suggesting additional functions of the peptide. Its presence in the latter, as well as the behavioral effects of exogenously administered LHRH, has led researchers to postulate the involvement of this peptide as a true transcriber in the control of reproductive behavior [R. Moss, "Fed. Proc." 36: 1978-1983 (1977)].
The existence of precursor forms of LHRH were suggested by chromatographic studies of hypothalamic and placental extracts. See J. Gautron, Id., and R. Millar et al., "Biochem. Biophys. Res. Commun." 74: 720-726 (1977). However, these forms were poorly characterized, present in impure mixtures and available only in extremely small quantities.
It has long been recognized that prolactin (PRL) secretion from the anterior pituitary is predominantly under inhibitory control. Although dopamine is known to exert such an inhibitory effect, it has been convincingly demonstrated that dopamine cannot be solely responsible for overall PRL inhibition. The existence of a major PRL-inhibitory factor (PIF) of peptidic nature has been invoked, but such a factor has not yet been characterized from hypothalamic extracts. Attempts to isolate hypothalamic PIF have shown that the areas containing dopamine-free PIF activity were located in the mediobasal hypothalamus and the organum vasculosum lamina terminalis [A. Enjalbert et al., "Neuroendocrinology" 24: 147-161 (1977)], regions which abound in LHRH-producing and secreting neurons. Preliminary purification studies from porcine and ovine hypothalamic tissue allowed size estimates for this activity of between 2000 and 8000 daltons [A. Enjalbert et al., Id.; A.P.S. Dharimal et al., "Endocrinology." 82: 1236-1241 (1968); and T. Greibrokk et al., "Biochem. Biophys. Res. Commun." 59: 704-709 (1974)]. Despite the time that has passed since these publications, the proteins responsible for PIF activity remain uncharacterized and unavailable in pure form.
Accordingly, it is an object of this invention to obtain DNA encoding such LHRH precursors and polypeptides which are coexpressed with LHRH as fusion proteins.
It is another object to identify a polypeptide capable of PIF activity.
It is a further object to synthesize such precursors and polypeptides in recombinant cell culture in large quantities and thereafter to obtain same in purified form.
It is another object to employ such precursors and polypeptides in analytical procedures, in the therapeutic modulation of reproductive cycles and in the treatment of prolactin-dependent tumors.
These and other objects will be apparent to the ordinary artisan from consideration of this specification as a whole.